Examples of machines having a plurality of load devices that are driven by an engine include working vehicles such as power shovels and wheel loaders. A working vehicle is usually provided with a traveling implement and a work implement.
For example, a technique disclosed in Patent Citation 1 is known as a technique relating to output control of an engine of a working vehicle. With this technique, the consumed horsepower of the traveling implement and work implement is measured at various points in time, and when the operator requests the speed of the work implement, an engine revolution speed is selected such that the work implement is operated at this speed. Where the operator does not request the speed of the work implement, the engine revolution speed is selected such that ensures the best fuel consumption efficiency at the consumed horsepower of the traveling implement and work implement.